A vehicle navigation system performs vehicle travel guidance for enabling a driver to easily drive the vehicle to a selected destination. Such a navigation system detects the position of the vehicle, reads out map data pertaining to an area at the vehicle current position from a data storage medium, for example, a CD-ROM (compact disk read-only memory), a DVD (digital versatile disc) or from a remote navigation server, and displays a map image on a monitor (display) screen while superimposing a mark representing the current location of the vehicle on a predetermined portion of the map image.
As the present position of the vehicle changes with the travel of the vehicle, the vehicle current position mark on the map image changes accordingly. Thus, navigation system enables the user to recognize the area at the vehicle position at a glance. When a destination is not set, such a navigation system functions as a locator map which indicates the current location of the vehicle on the map image. When the destination is set, the navigation system starts a route guidance function through a guided route from the starting point to the destination.
Typically, the route guidance function performs an intersection guidance process in which a monitor screen displays an enlarged intersection diagram and the direction in which the vehicle is to travel while displaying the guide route on a map. When a destination is input, a CPU in the navigation system automatically determines a most suitable guided route (calculated route) and successively stores nodes data (expressed in longitude and latitude) of the calculated route in a memory.
During actual traveling, the node data series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be discriminable from other routes. When the vehicle is within a predetermined distance from an intersection it is approaching, an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection is displayed to inform the user the direction of turn at the intersection.
FIG. 1A shows an example of the locator map display containing a vehicle current position mark VP on a map image 21. Typically, a navigation system shows the street on which the vehicle is running in the map image 21 and a name of the street in a message box 23 on the monitor screen. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen. In this manner, the locator map display shows the current position of the vehicle on the map image, however, it does not perform the route guidance function because the destination is not set in the navigation system.
FIG. 1B shows an example of the route guidance display for guiding the user to the destination. The route guidance display is activated after specifying the destination. In this example, the current street “W 190TH ST” and the left side of the street “PRAIRIE AVE” are highlighted in the map image 21. Thus, the navigation system indicates that the vehicle should make a left turn at the intersection. This example further shows an arrow indicating the direction (left) in which the vehicle is to turn at the intersection in a message box 22 at the top of the screen. The message box 22 also shows a name of the street which intersects with the current street and a distance to the intersection.
When a vehicle is in motion, setting the navigation functions poses a problem to a user. Actions for setting the navigation functions, such as finding points of interest (POI) or recently-used addresses, can be dangerous because such operation distracts the user's attention to driving. To operate the navigation system, the user must choose a desired entry from various categories or entries. This step requires the user to look at the monitor screen and find a desired entry from a plurality of categories or entries. Then, the user selects the entry on the monitor screen through input means such as a touch screen, a hardswitch on the panel, or a remote controller. Thus, for safe driving, a driver should be prohibited to operate the navigation system to a certain degree.
On the other hand, if the vehicle navigation system prohibits all the access to the navigation functions when the vehicle is in motion, the utility of the navigation system is diminished significantly. Such prohibition also frustrates the user since the user cannot use the navigation system unless the user stops the vehicle. Thus, overly limiting the access to the navigation functions can reduce the usefulness of the navigation system while allowing access to all functions will excessively distract the driver. Accordingly, the scope of access to the navigation functions must be balanced between the safety of driving and the usefulness of the vehicle navigation system.
In the conventional vehicle navigation system, access to the navigation system is mostly limited while the vehicle is in motion. In most cases, access to many functions of the navigation systems are simply locked out when the vehicle is in motion while allowing access to all of the functions when the vehicle is stationary. Thus, the user is unable to input new entries or change the entries in the navigation system at all when the vehicle is moving.
Even when the navigation system allows some access to the navigation functions, the scope of access is often arbitrary. For example, while the vehicle is in motion, a vehicle navigation system may allow the driver to select recently used addresses listed on the monitor while other functions are restricted. However, it is questionable whether this conventional approach achieves a balance between safety and usefulness.
For example, the conventional method does not take the surrounding driving conditions into account. When the vehicle is in motion, the surrounding circumstance and conditions change continuously. Speed, road conditions, and surrounding vehicles are examples that would affect the safety of driving and, thus, a scope of access to the navigation functions. There are other parameters, such as experience, age, physical conditions of the driver that affect the driving.
Accordingly, merely classifying whether the vehicle is in motion or stationary fails to provide adequate guideline for setting the scope of the access. Therefore, it is desirable to assign different degrees of access to the navigation functions based on the driving environment and conditions. For instance, when other vehicles are far away from the user's vehicle, the risk of traffic accident is relatively low and some vehicle navigation functions should be made available to the user.
Moreover, as described above, finding a desired entry out of a plurality of categories or entries, and selecting the entry through a touch-screen or other input means poses hardship to the user when the number of entries is large. The more the entries are available, the harder it becomes for the user to find a desired entry and to select it. Such distraction amounting to a relatively long time is undesirable while the vehicle is in motion. Thus, it is desirable to facilitate easy selection by reducing the number of allowable entries, thereby avoiding the distraction from the safe driving.